JP7709700B2 - Organic sludge dewatering agent - Google Patents

Description

The present invention relates to a water-soluble polymer that is widely used as a sludge dehydration agent, and more specifically, to a sludge dehydration agent containing a water-soluble polymer that has a deodorizing effect and improves sludge dehydration performance, and a sludge dehydration method using the same.

Water-soluble polymers are used as sludge dehydrating agents in the dehydration treatment of organic sludge, such as primary raw sludge settled from sewage, excess sludge or mixed raw sludge settled from effluent from an activated sludge tank, digested sludge obtained by subjecting these sludges to an anaerobic digestion treatment, or livestock sludge.
Polyacrylamide (PAM)-based water-soluble polymers are commonly used as sludge dehydrating agents, and sludge to which the sludge dehydrating agent has been added is dehydrated using an appropriate dehydrator such as a belt press or a screw press and treated as a dehydrated cake.
The sludge and dehydrated cake emit sulfur-based odors due to hydrogen sulfide, methyl mercaptan, etc., which can cause problems by worsening the working and living environments during the sludge dehydration process and the subsequent treatment processes. Therefore, the application of various compounds as deodorizers for sludge or dehydrated cake has been proposed.
For example, Patent Document 1 discloses a deodorizer for dehydrated cake using a 1,2-benzisothiazolin-3-one salt, and Patent Document 2 discloses a deodorizer for sludge or dehydrated cake containing 1,2-benzisothiazolin-3-one and a pyrithione compound.
Also, a method for preventing odor generation has been disclosed in which a deodorant and a polymer flocculant are used in a sludge dewatering process. Patent Document 3 discloses a method for preventing odor generation in which a metal salt of 2-mercaptobenzimidazole or a divalent metal salt of 2-mercaptobenzothiazole is added to sludge, and then a polymer flocculant is added.
Furthermore, a sludge dewatering agent containing a deodorant and a polymer flocculant is disclosed.
Patent Document 4 discloses an emulsion-type PAM polymer sludge dehydrating agent containing terpenes such as menthol and essential oils such as peppermint oil and eucalyptus oil as deodorants. Patent Document 5 discloses a polymer flocculant having a deodorant function, which is obtained by mixing a PAM polymer flocculant with humus soil having adsorbed p-dichlorobenzene or plant essential oils.
However, there are cases where a satisfactory deodorizing effect cannot be obtained, or where a high addition rate is required to obtain both the deodorizing and dehydrating effects. Therefore, there is a demand for a more efficient sludge dehydrating agent that has both the deodorizing and dehydrating effects.

Japanese Unexamined Patent Publication No. 6-134492 JP 2006-75704 A JP 2005-763 A Japanese Unexamined Patent Publication No. 59-173110 Japanese Unexamined Patent Publication No. 59-112811

The present invention relates to a sludge dehydrating agent used in sludge dehydration treatment, and aims to provide a sludge dehydrating agent and sludge dehydration method that have a deodorizing effect and higher performance.

As a result of intensive research to solve the above problems, we discovered that by using a sludge dehydration agent containing a water-soluble polymer with a specific composition and an isothiazolinone compound, it is possible to achieve a deodorizing effect and improved sludge dehydration performance, which led to the present invention.

By using the sludge dehydrating agent of the present invention, it is possible to improve the sludge dehydration performance by deodorizing or suppressing sulfur-based odors such as hydrogen sulfide and methyl mercaptan, which are the cause of odors in organic sludge that are causing problems due to bad odors.

The water-soluble polymer in the present invention has as its constituent units 1 to 99 mol % of a cationic monomer represented by the following general formula (1), 0 to 99 mol % of an anionic monomer represented by the following general formula (2), and 1 to 99 mol % of a nonionic monomer.
The cationic monomer represented by the general formula (1) is preferably 20 to 99 mol%, more preferably 30 to 99 mol%, and even more preferably 40 to 99 mol%. This is because a medium to high molar ratio of the cationic monomer is more versatile for different types of sludge. When the anionic monomer represented by the general formula (2) is contained, the anionic monomer is preferably 1 to 20 mol%, and more preferably 1 to 15 mol%.
General formula (1)
_R1 represents hydrogen or a methyl group, _R2 and _R3 represent an alkyl or alkoxy group having 1 to 3 carbon atoms, _R4 represents an alkyl or alkoxy group having 1 to 3 carbon atoms, an alkyl group having 7 to 20 carbon atoms, or an aryl group, A represents oxygen or NH, B represents an alkylene group having 2 to 4 carbon atoms, ^and _X1- represents an anion.
General formula (2)
_R5 represents _hydrogen , a methyl group or a ^{carboxymethyl} group, Q ^represents _SO3- ^, _C6H4SO3- , CONHC( _CH3 ) _{2CH2SO3- , C6H4COO- or COO-} , _{R6 represents} hydrogen or ^COOY2 , and _{Y1 and Y2} represent hydrogen ^or a cation.

Cationic monomers represented by the general formula (1) include quaternized products of dimethylaminoethyl (meth)acrylate or dimethylaminopropyl acrylamide with halides of lower alkyl groups such as methyl chloride or ethyl chloride. For example, (meth)acryloyloxyethyl trimethylammonium chloride, (meth)acryloyloxyethyl dimethylbenzylammonium chloride, (meth)acryloylaminopropyl trimethylammonium chloride, (meth)acryloylaminopropyl dimethylbenzylammonium chloride, (meth)acryloyloxy-2-hydroxypropyl trimethylammonium chloride, etc. Two or more of these may be combined. Anionic monomers represented by the general formula (2) include (meth)acrylic acid or its alkali metal salts or ammonium salts such as sodium salt, maleic acid or its alkali metal salts, acrylamidoalkanesulfonic acids such as acrylamido-2-methylpropanesulfonic acid or its alkali metal salts or ammonium salts, etc. Two or more of these may be combined.

The nonionic monomers used in the present invention include (meth)acrylamide, N,N'-dimethylacrylamide, acrylonitrile, 2-hydroxyethyl (meth)acrylate, diacetone acrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, acryloylmorpholine, etc. Among these, (meth)acrylamide is preferred. Two or more of these may be combined.

The water-soluble polymer of the present invention can be produced by a known method. It can be produced by copolymerizing one or more monomers or monomer mixtures selected from cationic monomers, nonionic monomers, and anionic monomers. The copolymerization is carried out by any polymerization method. For example, after polymerization by aqueous solution polymerization, water-in-oil emulsion polymerization, water-in-oil dispersion polymerization, dispersion polymerization in salt water, etc., the product can be in any form, such as an aqueous solution, a dispersion in salt water, a water-in-oil emulsion, or a powder. Among these, water-in-oil emulsion polymerization is preferred because it is easy to adjust the molecular weight and polymer structure.

In the case of a water-in-oil emulsion, it can be appropriately produced according to the methods described in JP-A-10-140496 and JP-A-2011-99076. That is, a monomer mixture containing one or more selected from cationic monomers, nonionic monomers, and anionic monomers is mixed with water, an oily substance consisting of at least a water-immiscible hydrocarbon, and at least one surfactant having an effective amount and HLB for forming a water-in-oil emulsion, and the mixture is stirred vigorously to form a water-in-oil emulsion, followed by polymerization.

Examples of oily substances made of hydrocarbons used as dispersion media include paraffins, naphthenes, mineral oils such as kerosene, light oil, and medium-weight oil, synthetic hydrocarbon oils having substantially the same range of boiling points, viscosity, and other properties as these, and mixtures of these. The content is in the range of 20% to 50% by mass, and preferably 20% to 35% by mass, based on the total amount of the water-in-oil emulsion.

An example of at least one type of surfactant having an effective amount and HLB for forming a water-in-oil emulsion is a nonionic surfactant with an HLB of 1 to 15, and specific examples include sorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate, polyoxyethylene nonylphenyl ether, etc. The amount of these surfactants to be added is 0.5 to 10% by mass, preferably 1 to 5% by mass, based on the total amount of the water-in-oil emulsion.

The polymerization concentration of the monomer is in the range of 20 to 60% by mass, and the polymerization concentration and temperature are set appropriately depending on the monomer composition and the selection of the initiator. The polymerization temperature is 20 to 80°C, preferably 20 to 60°C. A radical polymerization initiator is used to start the polymerization. These initiators may be either oil-soluble or water-soluble, and polymerization can be carried out with any of the azo, redox, and peroxide types. Examples of oil-soluble azo initiators include 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2-methylbutyronitrile), dimethyl-2,2'-azobis(2-methylpropionate), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile).

Examples of water-soluble azo initiators include 2,2'-azobis(amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-imidazolin-2-yl)propane] dihydrochloride, and 4,4'-azobis(4-cyanovaleric acid). Examples of redox initiators include combinations of ammonium peroxodisulfate with sodium sulfite, sodium hydrogensulfite, trimethylamine, and tetramethylethylenediamine. Examples of peroxide initiators include ammonium or potassium peroxodisulfate, hydrogen peroxide, benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, succinic peroxide, t-butylperoxy-2-ethylhexanoate, and t-butyl hydroperoxide.

A crosslinkable monomer can be used as a structural modifier during or after polymerization when producing the water-soluble polymer of the present invention. From the viewpoint of product stability when mixed with an isothiazolinone compound, a crosslinkable water-soluble polymer produced with the crosslinkable monomer present in the range of 0.00005 to 0.050 mass% relative to the total amount of monomers is preferred. Although this varies depending on the monomer composition and polymerization conditions, if it exceeds 0.050 mass%, crosslinking will proceed too far and the polymer will become water-insoluble, which is not preferred for the application of the present invention. Examples of crosslinkable monomers include N,N'-methylenebis(meth)acrylamide, triallylamine, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, polyethylene glycol di(meth)acrylate, N-vinyl(meth)acrylamide, N-methylallylacrylamide, glycidyl acrylate, polyethylene glycol diglycidyl ether, acrolein, glyoxal, vinyltrimethoxysilane, etc., with N,N'-methylenebis(meth)acrylamide being preferred.

In addition, it is effective to use isopropyl alcohol in an amount of 0.1 to 5% by mass relative to the monomer, or sodium formate in an amount of 0.01 to 0.5% by mass relative to the monomer, to adjust the degree of polymerization.

After polymerization, if necessary, a hydrophilic surfactant called a phase inversion agent is added to make the emulsion particles covered with an oil film more compatible with water and to make the water-soluble polymer inside more soluble, and the emulsion is then diluted with water for use in its intended purpose. Examples of hydrophilic surfactants include cationic surfactants and nonionic surfactants with an HLB of 9 to 15, such as polyoxyethylene polyoxypropylene alkyl ethers and polyoxyethylene alcohol ethers.

The water-soluble polymer in the present invention needs a certain molecular weight to perform as a sludge dehydration agent. In the present invention, the viscosity of a 4% by mass saline solution (SLV; viscosity of a 0.5% by mass salt solution) measured with a rotational viscometer at 25°C when the polymer is completely dissolved to a concentration of 0.5% by mass can be used as an index of molecular weight. The SLV of the water-soluble polymer in the present invention is preferably 5 mPa·s or more and 100 mPa·s or less, more preferably 10 mPa·s or more and 100 mPa·s or less, and even more preferably 10 mPa·s or more and 70 mPa·s or less. This 0.5% by mass salt solution viscosity is a value measured with a Brookfield viscometer using a No. 1 rotor at 60 rpm. As the Brookfield viscometer, a TVB-10M manufactured by Toki Sangyo or the like is used. The polymer solution is prepared by stirring at 800 rpm for 30 minutes.
The weight average molecular weight is preferably from 1 million to 8 million, more preferably from 2 million to 8 million, and even more preferably from 2 million to 6 million.

The isothiazoline compounds in the present invention are 1,2-benzisothiazolin-3-one, N-butyl-1,2-benzisothiazolin-3-one, 2-methylisothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 4,5-dichloro-2-methyl-4-isothiazolin-3-one, 2-ethyl-4-isothiazolin -3-one, 2-n-octyl-4-isothiazolin-3-one, 5-chloro-2-ethyl-4-isothiazolin-3-one, 5-chloro-2-t-octyl-4-isothiazolin-3-one, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one, and 4,5-dichloro-2-cyclohexyl-4-isothiazolin-3-one and their salts are used. Among these, 1,2-benzisothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one and their salts are preferred, and 1,2-benzisothiazolin-3-one and its salts are most preferred. This is because, when mixed with the water-soluble polymer of the present invention, the product stability tends to be higher than other isothiazoline compounds.

The water-soluble polymer and the isothiazolinone compound can be mixed by preparing an aqueous solution containing the isothiazolinone compound and then mixing it with the water-soluble polymer product. Alternatively, the isothiazolinone compound may be added to the water-soluble polymer solution, or an aqueous solution of the isothiazolinone compound may be prepared and then mixed with the water-soluble polymer solution. From the viewpoint of practicality, it is preferable to prepare an aqueous solution of the isothiazolinone compound and mix it with the water-soluble polymer product to obtain a sludge dehydration agent. In this case, it is preferable to contain the aqueous solution of the isothiazolinone compound in an amount of 1% by mass or less relative to the sludge dehydration agent product, although this depends on the aqueous solution concentration. This is because if the amount exceeds 1% by mass, problems may occur with the stability and solubility of the sludge dehydration agent product. The aqueous solution of the isothiazolinone compound is an isothiazolinone compound solution containing 50% by mass or more of water.

In the case where an aqueous solution containing an isothiazoline compound is prepared and then mixed with a water-soluble polymer product, the isothiazoline compound is first dissolved in the aqueous solution to an arbitrary concentration using a glycol such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, or polypropylene glycol; a glycol ether such as propylene glycol ether, diethylene glycol monobutyl ether, ethylene glycol ethyl ether, or ethylene glycol monobutyl ether; or an alcohol such as methanol, ethanol, propanol, or isopropanol.
In addition, an inorganic salt may be used or may be used in combination during dissolution. Examples of the inorganic salt include sodium chloride, potassium chloride, lithium chloride, sodium sulfate, potassium sulfate, sodium nitrate, potassium nitrate, sodium phosphate, potassium phosphate, calcium chloride, magnesium chloride, magnesium sulfate, sodium nitrate, calcium nitrate, magnesium nitrate, etc.

Furthermore, to adjust the pH of the isothiazolinone compound aqueous solution, one or more of sulfuric acid, hydrochloric acid, nitric acid, acetic acid, formic acid, sulfamic acid, citric acid, fumaric acid, phthalic acid, succinic acid, adipic acid, oxalic acid, malic acid, salicylic acid, or other acids or their salts, sodium hydroxide, potassium hydroxide, ferric sulfate, ferric chloride, ferric nitrate, copper sulfate, copper chloride, or hydrates thereof, can be added. Adjusting the pH of the isothiazolinone compound aqueous solution to 5.8 to 8.0 tends to improve the product stability and effect of the sludge dehydration agent of the present invention, which is preferable. These isothiazolinone compound aqueous solutions are mixed under any mixing conditions using a stirrer, mixer, homogenizer, etc. Forming a fine particle colloid by mixing is preferable because it further increases the diffusibility with the water-soluble polymer sample and improves the effect. It is preferable to adjust the isothiazolinone compound concentration in the isothiazolinone compound aqueous solution to 3 to 20 mass%.

In addition, the isothiazolin-based compounds used in the present invention may be those commercially available as general industrial raw materials. For example, "PROXEL (registered trademark) GXL" (20% by weight of 1,2-benzisothiazolin-3-one, dipropylene glycol solution) and "PROXEL (registered trademark) BDN" (35% by weight of 1,2-benzisothiazolin-3-one, dipropylene glycol solution) are available from Lonza Japan, and "ZONEN (registered trademark) FP" (a mixture of 11.2% by weight of 5-chloro-2-methyl-4-isothiazolin-3-one and 1.3% by weight of 2-methyl-4-isothiazolin-3-one, propylene glycol solution) is available from Chemiclear. Available examples include those available from Rohm and Haas Japan as "KATHON (registered trademark) LX1400" (a 10.6% by weight solution of 5-chloro-2-methyl-4-isothiazolin-3-one containing sodium nitrate) and those available from Rohm and Haas Japan as "KATHON (registered trademark) WT" (a 13.9% by weight mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in a 3:1 ratio, containing magnesium nitrate).

It is preferable to include 0.005 to 0.1% by mass of the isothiazolinone compound in the sludge dehydration agent product. If the amount is less than 0.005% by mass, the deodorizing and dehydration effects will not be significantly improved, and if the amount exceeds 0.1% by mass, the stability of the sludge dehydration agent product will be poor, which may cause problems with long-term storage.

The mechanism of action of the sludge dewatering agent in the present invention is unknown, but it is speculated that the odor component adsorption action is achieved by a chemical reaction between the sulfur-based odor components in the suspended solids in the sludge and the functional groups of the isothiazolinone compound, while the sulfur-based odor components that act as flocculation inhibitors are blocked, promoting the cross-linking adsorption action between the water-soluble polymer and the suspended solids in the sludge, improving the flocculation effect. In other words, it is believed that the effect of the sludge dewatering agent in the present invention is realized by the synergistic effect of the odor component adsorption action and the cross-linking adsorption action.

The types of sludge to which the sludge dehydrating agent of the present invention can be applied include excess sludge generated during biological treatment of wastewater from papermaking, chemical industry, food industry, etc., or organic sludge generated during treatment of urban sewage, human waste, and industrial wastewater (so-called raw sludge, excess sludge, mixed raw sludge, digested sludge, settling/floating sludge, and mixtures thereof), livestock sludge, etc., but it is particularly effective for organic sludge with a high organic content that is more difficult to dehydrate and more likely to cause odor problems. Specifically, the sludge has an organic matter content (VSS, loss on ignition of suspended solids, mass % to SS), which is an indicator of organic matter, of 45 mass % or more.
In recent years, there has been a tendency for these organic sludges to have increasing VSS and VTS (loss on ignition in the evaporation residue, mass % vs. TS), and since the effect of the sludge dehydration agent of the present invention is more pronounced compared to conventional sludge dehydration agents, sludge with a VSS of 60 mass % or more is preferred, and 70 mass % or more is even more preferred. Note that the various measured values are based on standard methods (sewage test methods).

The sludge dehydrating agent of the present invention is diluted with water to any desired concentration and added to the sludge. A range of 0.01 to 1.0% by mass is preferable. The addition rate to the sludge varies depending on the type of sludge and the dehydration model, but is 1 to 1000 ppm relative to the amount of sludge liquid. The type of dehydrator used can be a belt press, centrifugal dehydrator, screw press, multiple disk type dehydrator, rotary press, filter press, etc. Also, it may be used in combination with inorganic coagulants such as aluminum sulfate, aluminum chloride, polyaluminum chloride, polyferrous sulfate, polyferric sulfate, and ferric chloride.

The sludge dewatering agent of the present invention will be specifically described below, but the present invention is not limited to the following examples.

(Preparation of Water-Soluble Polymer Samples)
Water-soluble polymer samples A to C of the present invention were produced by the usual method for water-in-oil emulsions disclosed in JP-A-59-130397, JP-A-10-140496, JP-A-2011-99076, etc. These are products that are widely used as sludge dewatering agents. Their compositions and physical properties are shown in Table 1.

(Table 1)
Monomer; DMQ: acryloyloxyethyltrimethylammonium chloride, AAM: acrylamide, AAC: acrylic acid Form; EM: water-in-oil emulsion 0.2% by mass aqueous solution Viscosity: Viscosity (mPa·s) measured at 25° C. when dissolved in water to give a polymer concentration of 0.2% by mass.
Viscosity of 0.5% by mass saline solution: Viscosity (mPa·s) measured at 25° C. when the polymer is dissolved in 4% by mass saline solution to give a polymer concentration of 0.5% by mass.

(Preparation of aqueous solution of isothiazoline compound)
To a solution of 1,2-benzisothiazolin-3-one in dipropylene glycol, ferric sulfate heptahydrate, 10% by mass sodium hydroxide, and pure water were added in a ratio of 24:15:4:57% by mass, respectively, and mixed to prepare a 5% by mass aqueous solution (pH 6) of 1,2-benzisothiazolin-3-one.

Example 1
(Preparation of sludge dewatering agent)
The water-soluble polymer sample A in Table 1 was mixed with the aqueous solution of isothiazoline compounds prepared above to prepare sludge dehydration agent samples each containing 0.01 to 0.03% of isothiazoline compounds relative to the sludge dehydration agent product. Similarly, water-soluble polymer samples B and C were mixed with the aqueous solution of isothiazoline compounds to prepare sludge dehydration agent samples each containing 0.01 to 0.03% of isothiazoline compounds relative to the sludge dehydration agent product. These were used as sludge dehydration agents in the following practical test examples, which are designated as Example 1.

(Example Test 1, Sludge Dewatering Test)
A dehydration test was conducted on livestock sludge generated from a livestock farm (pH 7.2, electrical conductivity 146 mS/m, SS content 14,250 mg/L, VSS 89.5 mass%, VTS 87.5 mass%, M-alkalinity 562 mg/L, anion amount 5.81 meq/L).
200 mL of sludge was collected in a polybeaker, and a 0.2% by mass aqueous solution of a sludge dehydrating agent containing the water-soluble polymer sample A of Example 1 and 0.02% by mass of an isothiazolinone compound (sludge dehydrating agent product) was added at 200 ppm (polymer purity) relative to the sludge liquid volume, and the mixture was stirred upside down 10 times, filtered through a 40 mesh, and the amount of filtrate was measured. Then, the sludge was dehydrated for 30 seconds using a nylon filter cloth (#202) at a press pressure of 3 kg/ ^cm2 , and the cake moisture content (dried at 105°C for 20 hours) was measured. In addition, a similar test was carried out under similar conditions for the sludge dehydrating agent containing the water-soluble polymer sample B of Example 1 and 0.02% by mass of an isothiazolinone compound (sludge dehydrating agent product). These results are shown in Table 2.

(Comparative Test Example 1, Sludge Dewatering Test) Using the same sludge as in Test Example 1, a test similar to Test Example 1 was carried out using water-soluble polymer samples A and B in Table 1. The results are shown in Table 2.

(Table 2)

(Test Example 2, Odor Measurement Test)
200 mL of the same sludge as in Example 1 was collected in a polybeaker, and a 0.2 mass% aqueous solution of a sludge dehydration agent containing water-soluble polymer sample A of Example 1 and 0.02 mass% isothiazolinone compound (sludge dehydration agent product) was added at 100 ppm (polymer purity) relative to the sludge liquid volume. After stirring by inversion 10 times, 100 mL of sludge that had been filtered through a 40 mesh filter was placed in a 300 mL Erlenmeyer flask, the Erlenmeyer flask was sealed with a rubber stopper with a rubber tube attached and fixed in a 40°C water bath, and the hydrogen sulfide ( _H2S ) concentration after 3 hours was measured using a gas detector tube (manufactured by Gastec Corporation).
The same tests were also carried out under the same conditions for the water-soluble polymer sample B of Example 1 and a sludge dewatering agent containing 0.02% by mass of an isothiazolinone compound (based on the sludge dewatering agent product). The results are shown in Table 3.

(Comparative Test Example 2, Odor Measurement Test) Using the same sludge as in Test Example 1, a test similar to Test Example 2 was carried out using water-soluble polymer samples A and B in Table 1. The results are shown in Table 3.

(Table 3)

In the practical test examples 1 and 2 in which the sludge dehydrating agent of the present invention was added, the amount of filtered water was greater, the moisture content of the cake was lower, and the hydrogen sulfide concentration was lower than in the comparative test examples 1 and 2 in which the same type of water-soluble polymer sample was used, demonstrating that the dehydrating effect and deodorizing effect of the sludge dehydrating agent containing the water-soluble polymer and isothiazolinone compound of the present invention are excellent.

(Example 3, Sludge Dewatering Test)
A dehydration test was conducted on excess sludge generated from a food factory (pH 7.2, electrical conductivity 199 mS/m, SS content 11,750 mg/L, VSS 74.5 mass%, VTS 70.6 mass%, M-alkalinity 980 mg/L, anion amount 6.54 meq/L).
200 mL of sludge was collected in a polybeaker, and a 0.2% by weight aqueous solution of a sludge dehydrating agent containing the water-soluble polymer sample A of Example 1 and 0.01% by weight of an isothiazolinone compound (sludge dehydrating agent product) was added at 175 ppm (polymer purity) relative to the sludge liquid volume, and the mixture was transferred to a beaker and stirred 20 times, then filtered through a 40 mesh to measure the amount of filtrate. Then, the sludge was dehydrated for 60 ^seconds using a nylon filter cloth (#202) at a press pressure of 3 kg/cm2, and the cake moisture content (dried at 105°C for 20 hours) was measured. In addition, similar tests were carried out under similar conditions using other sludge dehydrating agent samples of Example 1. These results are shown in Table 4.

(Comparative Test Example 3, Sludge Dewatering Test) Using the same sludge as in Test Example 3, a test similar to Test Example 3 was carried out using water-soluble polymer samples A to C in Table 1. The results are shown in Table 4.

(Table 4)

(Example 4, Sludge Dewatering Test)
A dewatering test was conducted on froth sludge (pH 6.5, electrical conductivity 209 mS/m, SS content 81,500 mg/L, VSS 95.1 mass%, VTS 94.6 mass%, M-alkalinity 733 mg/L, anion content 4.85 meq/L) generated by pressure flotation from a food factory.
200 mL of sludge was collected in a polybeaker, and a 0.2 mass% aqueous solution of a sludge dehydrating agent containing the water-soluble polymer sample A of Example 1 and 0.01 mass% of an isothiazolinone compound (sludge dehydrating agent product) was added at 200 ppm or 350 ppm (polymer purity) relative to the sludge liquid volume, transferred to a beaker, stirred 20 times, filtered through a 40 mesh, and the amount of filtrate was measured. Then, the sludge was dehydrated for 60 seconds using a nylon filter cloth (#202) at a press pressure of 3 kg/ ^cm2 , and the cake moisture content (dried at 105°C for 20 hours) was measured. In addition, similar tests were carried out under similar conditions using other sludge dehydrating agent samples of Example 1. These results are shown in Table 5.

(Comparative Test Example 4, Sludge Dewatering Test) Using the same sludge as in Test Example 4, a test similar to Test Example 4 was carried out using water-soluble polymer sample A in Table 1. The results are shown in Table 5.

(Table 5)

(Example Test 5, Sludge Dewatering Test)
A dehydration test was conducted on excess sewage sludge generated from a livestock farm (pH 7.0, electrical conductivity 719 mS/m, SS content 17,500 mg/L, VSS 40.0 mass%, VTS 39.8 mass%, M-alkalinity 664 mg/L, anion amount 9.83 meq/L).
200 mL of sludge was collected in a polybeaker, and a 0.2% by weight aqueous solution of a sludge dehydrating agent containing the water-soluble polymer sample A of Example 1 and 0.02% by weight of an isothiazolinone compound (sludge dehydrating agent product) was added to the sludge liquid volume at 75 ppm (polymer purity), and the mixture was stirred by turning over 10 times, filtered through a 40 mesh, and the amount of filtrate was measured. Then, the sludge was dehydrated for 30 seconds using a nylon filter cloth (#202) at a pressing pressure of 3 kg/ ^cm2 , and the cake moisture content (dried at 105°C for 20 hours) was measured. In addition, similar tests were carried out under similar conditions using other sludge dehydrating agent samples of Example 1. These results are shown in Table 6.

(Comparative Test Example 5, Sludge Dewatering Test) Using the same sludge as in Test Example 5, a test similar to that in Test Example 5 was carried out using water-soluble polymer samples A and B in Table 1. The results are shown in Table 6.

(Table 6)

(Example 6, Sludge Dewatering Test)
A dehydration test was conducted on sludge generated from a pharmaceutical factory (pH 6.9, electrical conductivity 167 mS/m, SS content 21,500 mg/L, VSS 18.6 mass%, VTS 18.5 mass%, M-alkalinity 21 mg/L, anion amount 4.06 meq/L).
200 mL of sludge was collected in a polybeaker, and a 0.2% by mass aqueous solution of a sludge dehydrating agent containing the water-soluble polymer sample A of Example 1 and 0.02% by mass of an isothiazolinone compound (sludge dehydrating agent product) was added at 320 ppm (polymer purity) relative to the sludge liquid volume, and the mixture was transferred to a beaker and stirred 20 times, and then filtered through a 40 mesh to measure the amount of filtrate. Thereafter, the sludge was dehydrated for 60 seconds using a nylon filter cloth (T-1179L) at a press pressure of 3 kg/ ^cm2 , and the cake moisture content (dried at 105°C for 20 hours) was measured. Similar tests were also carried out under similar conditions using other sludge dehydrating agent samples of Example 1. These results are shown in Table 7.

(Comparative Test Example 6, Sludge Dewatering Test) Using the same sludge as in Test Example 6, a test similar to Test Example 6 was carried out using water-soluble polymer samples A to C in Table 1. The results are shown in Table 7.

(Table 7)

(Example 7, Sludge Dewatering Test)
A dehydration test was conducted on sewage sludge generated from a sewage treatment plant (pH 6.6, electrical conductivity 269 mS/m, SS content 2750 mg/L, VSS 90.0 mass%, VTS 76.5 mass%, M-alkalinity 790 mg/L, anion amount 1.30 meq/L).
200 mL of sludge was collected in a polybeaker, and a 0.2% by mass aqueous solution of a sludge dehydrating agent containing the water-soluble polymer sample C of Example 1 and 0.02% by mass of an isothiazolinone compound (sludge dehydrating agent product) was added at 40 ppm or 80 ppm (polymer purity) relative to the sludge liquid volume, and the mixture was transferred to a beaker and stirred 20 times, then filtered through a 40 mesh and the amount of filtrate was measured. Then, the sludge was dehydrated for 60 seconds using a nylon filter cloth (#202) at a pressing pressure of 3 kg/ ^cm2 , and the cake moisture content (dried at 105°C for 20 hours) was measured. These results are shown in Table 7.

(Comparative Test Example 7, Sludge Dewatering Test) Using the same sludge as in Test Example 7, a test similar to that in Test Example 7 was carried out using water-soluble polymer sample C or A in Table 1. The results are shown in Table 8.

(Table 8)

In the practical test examples 3 to 7 in which the sludge dehydrating agent of the present invention was added, the amount of filtered water was greater and the cake moisture content was lower than in the comparative test examples 3 to 7 in which the same type of water-soluble polymer sample was used, demonstrating that the sludge dehydrating agent containing the water-soluble polymer and isothiazolinone compound of the present invention has an excellent dehydrating effect for a wide variety of sludge.

(Test Example 8, Odor Measurement Test)
An odor measurement test was conducted on excess sewage sludge generated from a pig farm (pH 7.4, electrical conductivity 708 mS/m, SS content 23,500 mg/L, VSS 69.1 mass%, VTS 63.4 mass%, M-alkalinity 2,613 mg/L, anion amount 8.73 meq/L).
200 mL of sludge was collected in a polybeaker, and a 0.2% by mass aqueous solution of a sludge dehydrating agent containing the water-soluble polymer sample A of Example 1 and 0.02% by mass of an isothiazolinone compound (sludge dehydrating agent product) was added to the sludge liquid volume at 300 ppm (polymer purity), and the mixture was transferred to a beaker and stirred 20 times, after which 100 mL of sludge filtered through a 40 mesh was placed in a 300 mL Erlenmeyer flask, the Erlenmeyer flask was sealed with a rubber stopper with a rubber tube attached, and fixed in a 40°C water bath, and the hydrogen sulfide (H ₂ S) concentration after 2 hours was measured with a gas detector tube (manufactured by Gastec Co., Ltd.). In addition, similar tests were carried out under similar conditions using other sludge dehydrating agent samples of Example 1. These results are shown in Table 9.

(Comparative Test Example 8, Odor Measurement Test) Using the same sludge as in Test Example 8, a test similar to that in Test Example 8 was carried out using water-soluble polymer samples A and B in Table 1. The results are shown in Table 9.

(Table 9)

(Test Example 9, Odor Measurement Test)
An odor measurement test was conducted on raw sludge generated from a sewage treatment plant (pH 6.7, electrical conductivity 114 mS/m, SS content 6000 mg/L, VSS 87.5 mass%, VTS 84.6 mass%, M-alkalinity 260 mg/L, anion amount 1.48 meq/L).
200 mL of sludge was collected in a polybeaker, and a 0.2% by mass aqueous solution of a sludge dehydrating agent containing the water-soluble polymer sample A of Example 1 and 0.01% by mass of an isothiazolinone compound (sludge dehydrating agent product) was added to the sludge liquid at 100 ppm (polymer purity), and the mixture was transferred to a beaker and stirred 20 times. Then, 200 mL of the sludge filtered through a 40 mesh was placed in a 300 mL Erlenmeyer flask, the Erlenmeyer flask was sealed with a rubber stopper with a rubber tube attached, and fixed in a 40°C water bath. After 1 hour, the hydrogen sulfide (H ₂ S) and methyl mercaptan (CH ₃ SH) concentrations were measured with a gas detector tube (manufactured by Gastec Co., Ltd.). In addition, similar tests were carried out under similar conditions using other sludge dehydrating agent samples of Example 1. These results are shown in Table 10.

(Comparative Test Example 9, Odor Measurement Test) Using the same sludge as in Test Example 9, a test similar to that in Test Example 9 was carried out using water-soluble polymer samples A to C in Table 1. The results are shown in Table 10.

(Table 10)

In the implementation test examples 8 and 9 in which the sludge dehydrating agent of the present invention was added, the hydrogen sulfide or methyl mercaptan concentration was reduced compared to the cases in which the same type of water-soluble polymer sample was used in the respective comparison test examples 8 and 9, demonstrating that the deodorizing effect of the sludge dehydrating agent containing the water-soluble polymer and isothiazolinone compound of the present invention is excellent.

It has been confirmed that when the sludge dehydration agent containing the water-soluble polymer and isothiazolinone compound of the present invention is applied to a wide variety of sludges, particularly to organic sludges containing a large amount of organic matter, it can eliminate or suppress sulfur-based odors and improve sludge dehydration performance.

Claims (3)

A sludge dehydration agent comprising: 40 to 60 mol % of (meth)acryloyloxyethyltrimethylammonium chloride as a cationic monomer represented by the following general formula (1); 0 to 5 mol % of (meth)acrylic acid or an alkali metal salt such as a sodium salt or an ammonium salt thereof as an anionic monomer represented by the following general formula (2); and 40 to 55 mol % of (meth)acrylamide as a nonionic monomer; and 0.005 to 0.1 mass % of one or more isothiazoline compounds selected from 1,2-benzisothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, and 2-methyl-4-isothiazolin-3-one, based on the mass of the sludge dehydration agent product .
General formula (1)
_R1 represents hydrogen or a methyl group, _R2 and _R3 represent an alkyl or alkoxy group having 1 to 3 carbon atoms, _R4 represents an alkyl or alkoxy group having 1 to 3 carbon atoms, an alkyl group having 7 to 20 carbon atoms, or an aryl group, A represents oxygen or NH, B represents an alkylene group having 2 to 4 carbon atoms, ^and _X1- represents an anion.
General formula (2)
_R5 represents _hydrogen , a methyl group or a ^{carboxymethyl} group, Q ^represents _SO3- ^, _C6H4SO3- , CONHC( _CH3 ) _{2CH2SO3- , C6H4COO- or COO-} , _{R6 represents} hydrogen or ^COOY2 , and _{Y1 and Y2} represent hydrogen ^or a cation. 2. The sludge dewatering agent according to claim 1 , wherein the sludge dewatering agent is in the form of a water-in-oil emulsion. A method for dewatering sludge, comprising adding the sludge dewatering agent according to any one of claims 1 and 2 to sludge and dewatering the sludge.